WASHINGTON — The American effort to stem the flow of Iranian arms to Syria has faltered because of Iraq’s reluctance to inspect aircraft carrying the weapons through its airspace, US officials say.
The air corridor over Iraq has emerged as a main supply route for weapons, including rockets, antitank missiles, rocket-propelled grenades, and mortars.
Iran has an enormous stake in Syria, which is its staunchest Arab ally and has also provided a channel for Iran’s support to the Lebanese Islamist movement Hezbollah.
To the disappointment of the Obama administration, American efforts to persuade the Iraqis to conduct random inspections of the flights have been largely unsuccessful.
Secretary of State Hillary Rodham Clinton secured a commitment from Iraq’s foreign minister in September that Iraq would inspect flights from Iran to Syria. But the Iraqis have inspected only two, most recently on Oct. 27. No weapons were found, but one of the two planes that landed in Iraq for inspection was on its way back to Iran after delivering its cargo in Syria.
Adding to the United States’ frustrations, Iran appears to have been tipped off by Iraqi officials as to when inspections would be conducted, American officials say, citing classified reports by US intelligence analysts.
Iran’s continued efforts to aid the Syrian government were described in interviews with a dozen US administration, military and congressional officials, most of whom requested anonymity to discuss intelligence matters.
‘‘The abuse of Iraqi airspace by Iran continues to be a concern,’’ a US official said.
‘‘We urge Iraq to be diligent and consistent in fulfilling its international obligations and commitments, either by continuing to require flights over Iraqi territory en route to Syria from Iran to land for inspection or by denying overflight requests for Iranian aircraft going to Syria.’’
Iraqi officials insist that they oppose the ferrying of arms through Iraq’s airspace. They also cite claims by Iran that it is merely delivering humanitarian aid, and they call the American charges unfounded.
‘‘We wouldn’t be able to convince them, even if we searched all the airplanes, because they have prejudged the situation,’’ Ali al-Musawi, the spokesman for Prime Minister Nouri al-Maliki of Iraq, said of the American concerns. ‘‘Our policy is that we will not allow the transfer of arms to Syria.’’
Musawi acknowledged that one of the planes was not inspected until it was returning from Damascus, but said it was a simple error, not a deliberate effort to help the Iranians.
But one former Iraqi official, who asked not to be identified because he fears retaliation by the Iraqi government, said some officials in Baghdad had been doing the bare minimum to placate the United States and were in fact sympathetic to the Iranian efforts in Syria.
Iran’s support for Syria is vital to the Assad government, US officials said. In addition to flying arms and ammunition to Syria, Iran’s paramilitary Quds Force is sending trainers and advisers, sometimes disguised as religious pilgrims, tourists, and businessmen, the officials say.
In August, Defense Secretary Leon Panetta and General Martin Dempsey, chairman of the Joint Chiefs of Staff, criticized Iran for what they described as its assistance to the Assad government, in particular the training of a progovernment militia made up mostly of members of Assad’s minority Alawite sect.
‘‘Iran is playing a larger role in Syria in many ways, not only in terms of the IRGC, but in terms of assistance, training,’’ Panetta told reporters, referring to Iran’s Islamic Revolutionary Guards Corps. ‘‘We’ve got to make sure that Iran does not exercise that kind of influence in Syria.’’
There is evidence of collusion between Iranian and Iraqi officials on the inspections, according to US intelligence assessmen